Here's a look at the internal side of the drive chassis. The electrical interfaces line up and will snap in place quite easily once you slide the drive onto the chassis rail. The enclosure will come with flat head screws to hold the drive in place on the rail.

     To give us a hand with this project, Hitachi provided a pair of Deskstar drives. Each drive is of a different capacity but within the same product model lineup.  

     Reassembling the enclosure goes pretty quick. Just remember to reconnect the units faceplate light before you slide the chassis all the way into the enclosure. The frame is constructed with sturdy SECC steel, so there isn't any bending and once the drives are in place.